Thanks Shelley - that worked: to the extent that I restored the database.
However, I still have the same problem as kimble0938, writing under the heading '2Do chrashed' on 21 Nov:
"Every time, I will set a task as "done", 2Do crashed.
I tried a little bit: when the task has no repeating-announcement (week, day), everything is o.k.
But repeating-tasks will chrash, the status will not set as "done" and 2Do shuts down."
This was the initial problem that set me trying to restore in the first place, so a solution would be very welcome.